1. Field of the Invention
The present invention relates to a broadband wireless access communication systems, and more particularly to a method and a system for controlling a sleep mode in a broadband wireless access communication system.
2. Description of the Related Art
In conventional cellular networks, such as CDMA (Code Division Multiplex Access) and GSM (Global System for Mobile communication) networks, a sleep mode is realized by means of a slotted paging manner. That is, terminals operated in the conventional cellular networks may stay in a sleep mode having little power consumption if a terminal mode is not an active mode. In this state, the terminals often awake to check whether or not a paging message has been transmitted to the terminals. In a case in which the paging message has been transmitted to the terminals, the terminal mode is shifted from the sleep mode into the active mode. In addition, if the paging message is not transmitted to the terminals, the terminals enter into the sleep mode again.
At this time, since a paging slot is assigned between a base station and the terminals, each terminal awakes at a predetermined paging slot assigned thereto in order to check the paging message transmitted thereto. That is, a terminal in a CDMA network has an assigned paging slot and a terminal in a GSM network has an assigned paging group, so that it is enough for the terminals of the CDMA and GSM networks to awake once for a predetermined time period. Also, since the predetermined time period is fixed by a system, the system can easily manage the operation of the terminals.
However, it is difficult to control the sleep mode in a broadband wireless access communication system (called “4th generation communication system”) which has been actively studied and developed in order to support a high-speed service. The reason is that a sleep interval exponentially increases in the sleep mode proposed by an IEEE 802.16e communication system which is achieved by supplementing an IEEE 802.16a communication system with mobility of subscribers. That is, since the sleep interval exponentially increases in the IEEE 802.16e communication system, it is difficult for the IEEE 802.16e communication system to manage a start time of a sleep mode, a sleep interval, and an awaking point. Accordingly, it is difficult for the IEEE 802.16e to control the sleep mode.
FIG. 1 is a view schematically showing a procedure for controlling a sleep mode proposed by an IEEE 802.16e communication system. Conventionally, a sleep mode of the IEEE 802.16e communication system is started according to either a request of a subscriber terminal or a control command of a base station. FIG. 1 shows a method of starting the sleep mode according to the request the subscriber terminal request.
Referring to FIG. 1, a subscriber terminal 10 transmits a sleep request message (SLP-REQ message) to a base station 20 in order to enter into the sleep mode (S31). At this time, the subscriber terminal sends a required minimum size value (e.g., a min-window), a required maximum size value (e.g., a max-window), and a required value of a listening interval, which is a time slot where a corresponding terminal awakes to check whether a page message was transmitted to the subscriber terminal. A unit of each value is a frame.
Then, the base station 20 receiving the SLP-REQ message carries out a sleep time scheduling with reference to preset sleep control information (e.g. an admittable min-window, an admittable max-window, and an admittable listening interval) (S32). In addition, the base station 20 sends a sleep response message (SLP-RSP message) to the subscriber terminal 10 (S33). At this time, the base station transmits the number of frames remaining until the subscriber terminal 10 enters into the sleep mode (which is referred to start-time), a minimum time slot value (min-window value), a maximum time slot value (max-window), and a listening interval value, which are approved by the base station. In this case, a unit of each value is a frame.
Meanwhile, the subscriber terminal 10 receiving the SLP-RSP message enters into the sleep mode at the start time included in the SLP-RSP message (S34). Also, the subscriber terminal 10 awakes after the sleep interval elapses, and checks whether any packet data (PDU) has been transmitted from the base station 20. That is, the subscriber terminal 10 enters into the awake mode after the sleep interval has been passed (S35), and confirms a traffic indication message (TRF-IND message, also called a paging message) broadcasted from the base station 20 during the listening interval (S36). The TRF-IND message is information broadcast to the subscriber terminal 10 by the base station 20 and includes basic Connection IDentifiers (CIDs) of subscriber terminals receiving PDU data.
The subscriber terminal 10 determines whether or not its basic CID is included in the TRF-IND message so as to decide whether or not the subscriber terminal 10 should awake. That is, if a BCID of the subscriber terminal 10 is included in the received TRF-IND message, the subscriber terminal 10 will recognize the existence of PDU data that was transmitted to the subscriber terminal, and the subscriber terminal 10 will awaken. That is, if the TRF-IND message received by the subscriber terminal 10 is a positive traffic indication (S37), the subscriber terminal 10 performs a state transition into the active mode (S38).
In contrast, if the BCID of the subscriber terminal 10 is not included in the received TRF-IND message, the subscriber terminal 10 determines that no PDU data was transmitted to the subscriber terminal, the subscriber terminal 10 will enter the sleep mode again. That is, if the TRF-IND message received by the subscriber terminal 10 is a negative traffic indication, the state of the subscriber terminal 10 is shifted into the sleep mode (S34), and the base station 20 waits for the subscriber terminal 10 to awake during the sleep interval.
At this time, the subscriber terminal 10 increases the sleep interval to twice as long as the previous sleep interval, and keeps the sleep mode (S34) during the increased sleep interval. The subscriber terminal 10 repeatedly performs the sleep mode and the awake mode until the state of the subscriber terminal 10 is shifted into the active mode. Whenever the subscriber terminal 10 repeatedly performs the sleep mode and the awake mode, the subscriber terminal 10 increases the sleep interval to twice as long as the previous sleep interval in such a manner that the sleep interval reaches the maximum time slot allotted to the subscriber terminal 10 by the base station 20.
As described above, the IEEE 802.16e communication system executes a sleep mode while increasing the sleep interval twice as long as the previous sleep interval according to a sleep update algorithm. Accordingly, since the IEEE 802.16e communication system exponentially increases the sleep interval, it is difficult for the base station to integrally manage the sleep intervals of subscriber terminals.
Meanwhile, the IEEE 802.16e communication system defines three message types communicated between the subscriber terminal and the base station for allowing the subscriber terminal to enter into the sleep mode. That is, the three message types include a sleep request message (SLP-REQ message), a sleep response message (SLP-RSP message), and a traffic indication message (TRF-IND message).
FIGS. 2a to 2d show the format of messages communicated between the base station and the subscriber terminal in order to control the sleep mode, as described above. FIG. 2a shows a format of a sleep request message 40, FIG. 2b shows a format of a sleep response message 50a when rejecting sleep, and FIG. 2c shows a format of a sleep response message 50b when approving sleep. Also, FIG. 2d shows a traffic indication message format 60.
Referring to FIG. 2a, the SLP-REQ message 40 includes a management message type (MANAGEMENT MESSAGE TYPE; 8 bits) 41, a minimum window (MIN-WINDOW; 6 bits) 42, a maximum window (MAX-WINDOW; 10 bits) 43, and a listening interval (LISTENING INTERVAL; 8 bits) 44. The SLP-REQ message 40 is a dedicated message which is transmitted based on a connection identification (CID) of the subscriber terminal, and it is a message notifying that the subscriber terminal requests sleep.
At this time, the management message type (MANAGEMENT MESSAGE TYPE) 41 is information representing a type of a message which is currently transmitted. If the management message type is ‘45’ (MANAGEMENT MESSAGE TYPE=45), the currently transmitted message is the SLP-REQ message. The management message type 41 is realized with 8 bits.
The minimum window MIN-WINDOW (that is, a minimum time slot) 42 represents a requested start value for the sleep interval (measured in frames) and the maximum window MAX-WINDOW (that is, a maximum time slot) 43 represents a requested stop value for the sleep interval (measured in frames). That is, the sleep interval is updated and exponentially increases from the minimum window value 42 to the maximum window value 43.
The listening interval LISTENING INTERVAL 44 represents a requested LISTENING INTERVAL (measured in frames).
At this time, the minimum window 42, the maximum window 43, and the listening interval 44 are established as a frame unit.
Referring to FIG. 2b, the SLP-RSP message 50a used for rejecting a sleep request includes a management message type (8 bits) 51a, a sleep approval SLEEP-APPROVED (1 bit) 52a, and a reserved field RESERVED (7 bits) 53a. Such a SLP-RSP message 50a is also a dedicated message which is transmitted based on a connection identification (CID) of the subscriber terminal. The SLP-RSP message 50a is a message for determining a sleep timing of the subscriber terminal after the base station scheduling a sleep time of the subscriber terminal.
At this time, the management message type 51a represents a type of a currently transmitted message. If the management message type is ‘46’ (MANAGEMENT MESSAGE TYPE=46), the currently transmitted message is the SLP-RSP message.
The sleep approval (SLEEP-APPROVED) 52a is represented with one bit. The sleep approval 52a ‘0’ represents that it is impossible to shift into the sleep mode (SLEEP-MODE REQUEST DENIED).
The reserved field (RESERVED) 53a is a field reserved for other use.
Referring to FIG. 2c, when the base station approves the sleep request, the SLP-RSP message 50b transmitted to the subscriber terminal includes a management message type (8 bits) 51b, a sleep approval (SLEEP-APPROVED: 1 bit) 52b, a start time (START-TIME: 7 bits) 53b, a minimum window (MIN-WINDOW) 54b, a maximum window (MAX-WINDOW) 55b, and a listening interval (LISTENING INTERVAL) 56b. 
At this time, the management message type 51b represents a type of a currently transmitted message. If the management message type is ‘46’ (MANAGEMENT MESSAGE TYPE=46), the currently transmitted message is the sleep response message.
The sleep approval (SLEEP-APPROVED) 52b is represented with one bit. The sleep approval ‘1’ (SLEEP-MODE REQUEST APPROVED) represents that it is possible to shift into a sleep mode.
The start time START-TIME 53b is frame values before the subscriber terminal enters into the first sleep interval (the first SLEEP INTERVAL), in which a value of a frame receiving the sleep response message is not included in the frame values. That is, the subscriber terminal will perform the state transition into the sleep mode after both a frame next to the frame during which the sleep response message is received and one or more of the adjacent frames, as specified by the START-TIME elapse.
The minimum window 54b represents a start value for the SLEEP INTERVAL (measured in frames), and the maximum window 55b represents a stop value for the SLEEP INTERVAL (measured in frames). The listening interval 56b is a value for LISTENING INTERVAL (measured in frames).
Referring to FIG. 2d, the TRF-IND message 60 includes a management message type (8 bits) 61, the number of positive subscribers NUM-POSITIVE (8 bits) 62, and connection identifications of the positive subscribers (CIDs 63 and 64), each of which is represented by 16 bits. Such a TRF-IND message 60 is transmitted in a broadcasting method, which is different from the transmitting methods for the SLP-REQ message and the SLP-RSP message.
First, the management message type 61 represents a type of a message which is currently transmitted. The management message type 61 ‘47’ (MANAGEMENT MESSAGE TYPE=47) represents that the currently transmitted message is the TRF-IND message.
The number of the positive subscribers 62 represents the number of subscriber terminals to which packet data must be transmitted. The connection identifiers (CIDs 63 and 64) of the positive subscribers include connection identification information corresponding to the number of the positive subscribers.
FIG. 3 explains a sleep interval update algorithm which is proposed for the IEEE 802.16e communication system. In FIG. 3, ‘SS’ refers to a subscriber terminal and ‘BS’ refers to a base station. Also, boxes including ‘SS’ and ‘BS’ refer to frames.
Referring to FIG. 3, the subscriber terminal SS requests the sleep mode to the base station BS in an nth frame (S71) and the base station BS responds to the request for the sleep mode in n+1th frame (S72) by specifying the start time of the sleep mode as n+3th frame. In this case, the subscriber terminal SS repeats the sleep interval and the listening interval. As shown in FIG. 3, an initial sleep interval has 2 frames, and a second sleep interval has 4 frames which are double to the number of frames of the initial sleep interval.
As described above, in the conventional IEEE 802.16e communication system, since subscriber terminals request sleep at different points of time and sleep intervals of subscriber terminals exponentially increase, it is difficult for the base station to manage the sleep intervals of the subscriber terminals and to manage the subscriber terminals by grouping the subscriber terminals.